MicroRNAs (miRNAs) are evolutionarily conserved small non-coding RNAs, which regulate gene expression in a sequence-specific manner. The potential regulatory circuitry afforded by miRNA is enormous. Rapidly accumulating evidence indicates that miRNAs play critical roles in cancer. Our earlier findings that miRNAs exhibit genomic alterations at high frequency and their expression is remarkably deregulated in ovarian and breast cancers, strongly suggest that miRNAs are involved in the initiation and progression of cancer. Therefore, investigation of miRNA function in cancer will provide novel strategies for both diagnosis and treatment of cancer patients. Our preliminary studies have identified mir-30d as a potential oncogene. First, mir-30d plays a critical role in both epithelial transformation and established epithelial tumor growth. Second, mir-30d may directly regulate certain cancer-associated pathways. Third, the DNA copy number of mir-30d is frequently amplified in multiple types of human epithelial tumors. Meanwhile, overexpression of mir-30d is significantly associated with poor clinical outcome in ovarian cancer patients. Forth, pre-mir-30d is induced by hypoxia and prevents tumor cells from apoptosis. Finally, mir-30d inhibitor treatment is capable to remarkably reduce tumor cell growth. We hypothesize that mir-30d plays a critical role in breast and ovarian epithelial malignant transformation and tumor development. Specific Aim 1: Define the molecular mechanism of mir-30d in preventing hypoxia-induced apoptosis. We will dissect the transcriptional regulation of mir-30d under hypoxia and map the prosurvival pathways downstream of mir-30d. Specific Aim 2: Examine the function of mir-30d in preventing hypoxia-induced apoptosis in vivo. We will examine the function of mir-30d in vivo in a novel tetracycline-inducible human tumor xenograft model and a large collection of human ovarian and breast tumor specimens. Specific Aim 3: Investigate the role of mir-30d in tumorigenesis. We will examine the early transformation ability induced by mir-30d activation in vivo. After having completed the proposed studies, we will be able to test mir-30d targeted therapy using mir-30d ASO in pre-clinical animal models. If successful, our long-term goal is to commence phase I/II clinical trials in ovarian cancer patients using mir-30d ASO. PUBLIC HEALTH RELEVANCE: Ovarian and breast cancers are the most important causes of cancer-related mortality in women. microRNAs are small non-coding RNAs, which regulate gene expression in a sequence-specific manner. We will conduct a detailed study of mir-30d in ovarian and breast cancer with the intent to (i) learn important lessons in ovarian and breast cancer biology;(ii) discover novel therapeutic target.